Electronic light generating element light bulb

ABSTRACT

The present system for driving an electronic light generating element, includes: (i) input terminals, (ii) an input circuit coupled to the input terminals and operable to convert a sinusoidal signal to a signal independent of negative current attributes, (iii) a switch control circuit coupled to the input circuit and operable to generate a switching signal having pulses, and (iv) a switching element coupled to the input circuit and the switch control circuit. The switching element is operable to generate an output signal formed as a series of bursts having peak amplitudes above a maximum forward current rating for a duty cycle less than a maximum operating duty cycle over which an electronic light generating element may be catastrophically damaged in response to the signal independent of negative current attributes and switching being applied to the switching element. The output signal is applied to the electronic light generating element to produce light.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from co-pending U.S. Provisional PatentApplication Ser. No. 60/565,268 titled “Improved Electronic LightGenerating Element Light Bulb” and filed 23 Apr. 2004, the entireteachings of which are herein incorporated by reference. In addition,this application is related to U.S. patent application titled “LightingElement Using Electronically Activated Light Emitting Elements AndMethod Of Making Same,” U.S. Patent Application titled “light bulbhaving wide angle light dispersion and method of making same,” and U.S.Patent Application titled “Light Bulb Having Surfaces For ReflectingLight Produced By Electronic Light Generating Sources,” both filed onthe same date hereof, the entire teachings of which are hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The principles of the present invention are generally directed to alight bulb, and more particularly, but not by limitation, to a lightbulb using electronic light generating elements, such as LEDs, andhaving circuitry for over-driving the electronic light generatingelements to produce a perceived higher amount of light.

2. Description of Related Art

Since the invention of the light bulb by Edison, light bulbs have becomepervasive throughout society. Light bulbs have evolved for all sorts ofuses as technology for generating light has developed. Initially, anincandescent light bulb that uses a metal filament placed inside a glassbulb forming a vacuum was developed. The incandescent light bulboperates by driving current through the filament to cause the filamentto heat up and produce light. While the incandescent light bulb iseffective in producing large amounts of light, these light bulbs arevery inefficient in that a substantial portion of the energy used togenerate the light is immediate converted into heat. The inefficient useof energy is expensive and the resulting heat is generally undesirableas it can cause an individual handling the lit light bulb to receive aburn injury, especially with higher wattage light bulbs. In applicationswhere many incandescent light bulbs are used to illuminate an occupiedspace (e.g., casinos, malls, retail environments, work environments,etc.), additional cooling is needed to maintain a comfortabletemperature for people within that setting due to the heat produced bythe lighting. Another limitation of a conventional incandescent lightbulb is its limited life span. The life span problem is particularlyproblematic in applications where the light bulb is not readilyaccessible, such as in high locations or in complex fixtures, andrequires manual labor and/or machine support for changing the lightbulb. For example, changing traffic light bulbs, particularly thosesuspended from wires or located at a higher elevation, is a particularlydifficult and expensive task as it requires both labor and a specializedvehicle having a lift for raising someone to a height of the trafficlight to change the light bulbs.

A light emitting device developed after the incandescent light bulb is afluorescent light emitting device. Fluorescent light is generallyproduced by creating electric arcs inside a gas-rich tube to produceultraviolet light. The ultraviolet light is converted to visible lightby passing the ultraviolet light through a layer of phosphor on theinside of the glass tube to cause the phosphor to glow white.Fluorescent lights have traditionally been produced in tubes having anelectrode at each end for creating the electric arcs within the gasfilled tube. However, more recently, fluorescent light bulbs have beendeveloped to be compatible with an Edison-based socket and shaped as alight bulb. While the fluorescent light bulb is an improvement of theincandescent light bulb in terms of having a longer life span, the useof the fluorescent light bulb is still commercially limited due to anumber of factors, including: objectionable color, efficiency concerns,limited configurations, environmental concerns, and limited life spans.

More recently, solid-state light emitting devices have been developedfor light bulbs and flashlights. One such solid-state light emittingdevice is a light emitting diode (LED). LEDs overcome many of theproblems that are found in incandescent and fluorescent lightingsystems. LEDs are more durable, do not require a glass vacuum, producesignificantly lower heat than any non-solid state lighting devices, and,thus, have a longer life span. However, LEDs have certain limitingfactors and, thus, have not been commercially viable for general purposelighting. Such limitations include narrow illumination beam widths athigher efficiency outputs, ultra-narrow frequency bandwidths, and lowerluminance output.

Light emitting diodes are solid-state devices and produce light when anelectric current passes through the device and causes electrons torecombine with holes, thereby emitting photons at a PN junction of twodifferently doped substrates, one negatively charged (N-type substrate)and one positively charged (P-type substrate). When current is appliedto the LED and flows across the PN junction, the junction heats up. If acurrent exceeds a maximum specified forward current for a long enoughduration of time, as defined by a manufacturer of the LED, acatastrophic failure causing complete or partial damage to thefunctionality of the LED may result.

To increase the brightness of LEDs while lowering the temperature of thePN junction, manufacturers of LEDs have spent much research anddevelopment time and money in producing different heat sinks andmaterials. Reducing the PN junction temperature improves performance ofan LED as more current can be applied to the LED to produce more lightwithout burning out the LED. While the performance of the LED hasgreatly improved by the use of different materials, users of LEDs mustdrive the LEDs within a manufacturer's specification to avoid damagingthem in whole or part. The limiting factor of LED operation is the PNjunction temperature. So as to not burn out an LED, the conventionaltechnique for powering an LED includes applying a DC current below amaximum (average) forward current, which is the maximum average amountof current the LED is able to conduct in a forward bias mode. Themaximum forward current for typical LED devices is about 20–30 milliamps(mA), though it may vary beyond this range. In the case of the maximumforward current being 20 mA, for direct current (DC) applications toproduce a maximum illumination from the LEDs, a DC current of 19.5 mAmay be used. While this technique is effective in minimizing burnout toprotect the LEDs, the limited amount of luminance produced by thistechnique is not necessarily satisfactory for many applications using anLED light bulb. To increase the amount of illumination of the LED lightbulb using a DC driving technique, manufacturers increase the number ofLEDs within a single bulb structure. While the increased number of LEDsimproves the light intensity of the overall light bulb, it alsoincreases cost and size of the LED light bulbs, thereby reducingcommercialization potential of the LED light bulb.

In order to reduce the thermal problems of the PN junction of the LEDdevices, some manufacturers have used pulse width modulation (PWM) todrive the LEDs. Pulse width modulation is a technique for driving asignal that alters the width of a pulse to change a duty cycle (i.e.,ratio of ON time to OFF time within a period). By using a duty cycleless than 100 percent as is the case of using the DC driving technique,the PN junction temperature may be reduced. The human eye is generallyincapable of noticing flicker of a light strobing at or above 100 pulsesper second. The pulse width modulation driving technique typicallyoperates at 100 Hz maintains a duty cycle of 30 and 60 percent orhigher. This reduced duty cycle from the DC driving technique, which hasa 100 percent duty cycle, maintains a lower PN junction temperature.While using pulse width modulation is an inexpensive way to convert AClight bulb applications to DC light bulb applications, the LEDbrightness remains limited by the PN junction temperature. In otherwords, by using pulse width modulation, an effective average currentresults such that the PN junction temperature remains below a thermaltemperature that causes the LEDs to catastrophically fail. Pulse widthmodulation driving devices are widely available and serve as a goodmidpoint solution. However, as the duty cycle employed in pulse widthmodulation driving techniques exceed peak current ratings of LEDmanufacturers by 200 to 600 percent, pulse width modulation suppliesand/or drivers cannot drive the LED to their maximum output withoutencountering the same failure mode associated with DC supplies.

Manufacturers of white LED light bulbs typically use blue or ultravioletLEDs for generating light and use a phosphor coating on the lenses orabove the wafer of the LEDs to produce visible white light similar to afluorescent light bulb. However, such a configuration causes a loss ofoutput efficiency because phosphor tends to backscatter the lightproduced by the LEDs. Also, the life of the LED light bulbs withphosphor is diminished because phosphor has a more limited lifeexpectancy than the underlying light emitting diode. Finally, as withthe fluorescent light bulb, color of the produced light is objectionablefrom a commercial standpoint and degrades over time.

A structural disadvantage of conventional LED light bulbs results fromthe use of transformers as a DC power source for driving the LEDs with alower voltage. The use of the transformer requires the use of a largebase for the LED light bulb, thereby making the conventional LED lightbulbs incapable of fitting into a conventional light socket and/orhaving a less appealing appearance to consumers.

SUMMARY OF THE INVENTION

The heating, inefficiency, and color problems of incandescent andfluorescent light bulbs and lack of brightness, objectionable color, andunappealing physical appearance of conventional LED light bulbs areovercome by the principles of the present electronic light generatingelement light bulb which utilizes a circuit that does not include atransformer, uses a circuit to overdrive electronic light generatingelements to produce a higher perceived amount of light, and may includeat least three different colors to produce a desired color of whitelight. In one embodiment, the electronic light generating elements arelight emitting diodes capable of producing light or any othersolid-state device to have significantly improved efficiency and thermalcharacteristics over incandescent, fluorescent, or other traditionallight bulbs. By driving the electronic light generating elements with aseries of pulses, PN junction temperature that is typically the limitingfactor remains lower and a higher number of pulses per second, such as a1000 pulses per second, of overdrive current may be applied to theelectronic light generating elements without causing a catastrophicfailure thereof.

The principles of the present electronic light generating element lightbulb include a circuit and a method for driving an electronic lightgenerating element. The circuit may include (i) an input circuitoperable to convert a sinusoidal signal to a signal independent ofnegative current attributes, (ii) a switch control circuit coupled tothe input circuit and operable to generate a switching signal havingpulses, and (iii) a switching element coupled to the input circuit andthe switch control circuit. The switching element is operable togenerate an output signal that is formed of a series of bursts havingpeak amplitudes above a maximum forward current rating for a duty cycleless than a maximum operating duty cycle over which an electronic lightgenerating element may be catastrophically damaged in response to (a)the signal independent of negative current attributes and (b) switchingbeing applied to the switching element. The output signal is applied tothe electronic light generating element to produce light.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed invention is described with reference to the accompanyingdrawings, which show sample embodiments of the invention and which areincorporated in the specification hereof by reference, wherein:

FIG. 1A is an illustration showing an exemplary electronic lightgenerating element light bulb (“electronic light bulb”);

FIG. 1B is an illustration of a front view of the electronic light bulbof FIG. 1A;

FIG. 1C illustrates an inside, front view of a base of the electroniclight bulb of FIG. 1A showing an electronic circuit board having acircuit mounted thereto;

FIG. 2 is a block diagram representing circuits or modules formed ofelectronic components of an electronic light bulb;

FIG. 3A is a schematic of an exemplary circuit for performing thefunctions of the modules of FIG. 2;

FIG. 3B is a schematic of a circuit performing the functions of themodules of FIG. 2 that further includes interacting with a dimmer asunderstood in the art for increasing and decreasing the light output(luminance) of the electronic light generating elements of theelectronic light;

FIG. 4A illustrates an exemplary pulse train for driving and dimmingelectronic light generating elements by altering the amplitude of thepulses of the pulse train of FIG. 4A;

FIG. 4B illustrates exemplary output signals produced by the switchingelement that correspond to the pulses;

FIG. 5A illustrates an exemplary pulse train for driving and dimmingelectronic light generating elements by decreasing the frequency of thepulse train;

FIG. 5B illustrates exemplary output signals produced by the switchingelement that correspond to the pulses of the pulse train of FIG. 5A; and

FIG. 6 illustrates a CIE chromaticity diagram as understood in the art.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1A is an illustration showing an exemplary electronic lightgenerating element light bulb (“electronic light bulb”). The electroniclight bulb 100 includes a housing formed of a tapered wall 102 and anouter cap 104. Although shown as a tapered wall 102, it should beunderstood that other non-tapered or more tapered configurations maybeutilized in forming the housing of the electronic light bulb 100. In oneembodiment, the outer cap 104 is translucent. Alternatively, the outercap 104 may be clear. Still yet, in another embodiment, the outer cap104 may be formed of a lens that focuses, defocuses, diffuses, narrows,broadens, or performs some other optical function to the light beinggenerated by electronic light generating elements within the electroniclight bulb 100. The housing may further include a base 106 that engagesor is coupled to the outer wall 102. The base 106 may be formed as a“Edison base” for connection to a conventional lamp device or the likecapable of receiving electronic light bulbs having Edison bases. Itshould be understood that the base 106 may be shaped in otherconfigurations for use in different standard-type or proprietarysockets. The base 106 may be externally threaded having threads 108 forscrewing the electronic light bulb 100 into a socket of a light fixture.Other mounting configurations, such as a bayonet-type configuration, maybe utilized in accordance with the principles of the present invention.

A contact 110, which is coupled to or disposed in relation to the base106, may be electrically coupled to a post or stem 112 that supports acircuit board 114 having electronic light generating elements 116mounted thereto. In another embodiment, a circuit board (see FIG. 1C)may be disposed in the base 106 (see FIG. 1C) and signals produced bythe circuit board may be communicated to the circuit board 114 to powerthe electronic light generating elements 116. The stem 112 may beelectrically conductive or may guide one or more electrical conductorsfrom the contact 110 to the circuit board 114 to conduct electricalpower and/or electronic signaling thereto. The stem at 112 further maybe utilized to align or position the circuit board 114 in relation tothe outer cap 104.

The electronic light generating elements may be light emitting diodes(LEDs). The light emitting diodes may be conventional light emittingdiodes or organic light emitting diodes (OLEDs) as understood in theart. Alternatively, the electronic light generating elements may be anydevice, solid-state or otherwise, that is electronically activated toproduce light. As understood in the art, organic and inorganic crystalsmay be electronically activated to generate a light and is encompassedby the term, “electronic light generating elements”.

FIG. 1B is an illustration of a front view of the electronic light bulb100. As shown, the outer wall 102 engages the outer cap 104, which islocated optically in front of the electronic light generating elements116. The electronic light generating elements 116 may be configured inrows and columns on the circuit board 114 (FIG. 1A). In one embodiment,the electronic light generating elements 116 include three colors thatmay be utilized to produce white or any other color of light based onblending colors produced by each of the electronic light generatingelements 116. For example, the colors of red, green, and blue (RGB),which are primary colors, may be selected to be included in theelectronic light bulb 100. As shown, groups of three electronic lightgenerating elements 116 a, 116 b, and 116 c (collectively 116) may bearranged in close proximity to one another to form a “pixel” of theelectronic light bulb 100. By turning each of these electronic lightgenerating elements 116 a–116 c on for a predetermined duration of time,the electronic light bulb 100 may produce a white light directly fromthe electronic light generating elements 116 rather than using aphosphor or other coating to produce the white light. By directlyproducing white light from the LEDs and avoiding the use of phosphor,for example, the life span of the electronic light bulb 100 is limitedto the lifespan of the LEDs and not the coating.

It should be understood that the proximity of the different colors ofelectronic light generating elements 116 may be configured in manydifferent ways based on the desire of the designer of the electroniclight bulb 100 or the application therefor. The colors of the electroniclight generating elements 116 may be selected by the designer ormanufacturer and populated in the electronic light 100 for a particularapplication, including environmental applications. For example, to avoidattracting certain bugs, electronic light generating elements that emitwavelengths greater than 490 nm, which is the highest wavelength certainbugs can see, may be used. In another example, to kill microorganisms,such as bacteria, electronic light generating elements that produceultraviolet light may be selected. It should also be understood that theelectronic light generating elements 116 may be configured in a non-rowand column configurations, such as a circular, oval, or other geometricor non geometric configuration. Still yet, while the use of three ormore primary colors for producing white or other colors of light may beutilized in accordance with the principles of the present invention,conventional one or two color electronic light generating elements 116may be utilized in accordance with increasing the brightness of theelectronic light generating elements 116 as described further herein,but have lifetime and color limitations as previously described.

FIG. 1C illustrates an inside, front view of the base 106 showing anelectronic circuit board 118 having a circuit 120 mounted thereto. Thecircuit 120 may include circuitry for receiving power from the contact110 and generate signals for controlling the electronic light generatingelements 116 (FIG. 1A). The electronic circuit board 118 may be mountedwithin the base 106 so as to be substantially visually undetectable byan observer of the electronic light bulb 100. However, it should beunderstood that the electronic circuit board 118 may be mounted to thecircuit board 114 or part of or the entire circuit 120 may be integratedonto the circuit board 114 so as to collocate the circuit 120 with theelectronic light generating elements 116.

FIG. 2 is a block diagram representing circuits or modules 200 formed ofelectronic components of an electronic light bulb. The modules 200include a circuit protection and input filter circuit 202, switch timingand control circuit 204, switch and modulator circuit 206, and outputand ripple correction circuit 208. A light emitting diode array 210 iselectrically coupled to the output and ripple correction circuit 208. Asunderstood in the art, the modules 200 may be formed by one or moreelectronic components.

As shown, the circuit protection and input filter circuit 202 receivesan input signal 212 from an alternating current (AC) source 214. The ACsource 214 may be power delivered from a wall socket (not shown) intowhich a lamp or other light fixture is plugged. The input signal 212 maybe a substantially sinusoidal signal of 50 Hz, 60 Hz, or otherwisedepending upon the country, for example. A rectified signal 216 producedby the circuit protection and input filter circuit 202 may be generatedfrom the input signal 212 and have no negative voltage or current.

The switch timing and control circuit 204 provides an input to theswitch and modulator circuit 206 as does the circuit protection andinput filter circuit 202. An output of the switch and modulator circuit206 may be a substantially periodic pulse train 218. The pulse train maybe formed of individual pulses that are amplitude modulated. In otherwords, the amplitudes of each pulse may be raised or lowered dependingon the amount of current desired to be input to the output and ripplecorrection circuit 208 for driving the light emitting diode array 210.An output signal 220 is shown as a substantially periodic bursts fordriving the light emitting diode array 210. By driving the lightemitting diode array 210 using the output signal 220 having a series ofsubstantially periodic bursts, the LEDs of the light emitting diodearray 210 are driven to a maximum luminance output, which is higher thancan be achieved by using conventional pulse width modulation drivingtechniques that may have a thirty percent duty cycle, for example,because the output signal 220 has a duty cycle of at most ten percent.It should be understood that the maximum duty cycle for the outputsignal 220 may be increased or decreased based on the specifications ofthe electronic light generating elements selected for the electroniclight bulb.

The modules 200 are capable of handling changes in line or supplyvoltage and/or different AC frequencies. Changes in line voltage have amoderately linear effect on the output signal 220. This linear effectmay be stabilized by inserting higher value capacitors in the output andripple correction circuit 208. A voltage swing of 20 percent or greatercan result in the light either shutting off (flickering) if the voltageswing is momentary or shutting off as the fuse opens if heavyover-voltage is present. These are both unusual scenarios in the UnitedStates power grid, but are issues of concern in other parts of theworld. Operating voltages of 95V–140V should not adversely affectperformance. It should be understood that the principles of the presentinvention may include power supplies configured for markets thatnominally use 100V, 220V, 240V, or any other voltage level.

FIG. 3A is a schematic of an exemplary circuit 300 a for performing thefunctions of the modules 200 of FIG. 2. Each of the modules 202, 204,206, and 208 are shown by dashed lines around circuitry for performingthe functions of the modules 200.

The circuit protection and input filter circuit 202 includes a pair ofinput terminals 302 a and 302 b (collectively 302), a fuse 304, andbridge rectifier 306. The fuse 304 is optional, but may be utilized toprevent damage from an over-current surge to the rest of the circuit 300a. The bridge rectifier 306 may be composed of zener diodes asunderstood in the art. The bridge rectifier 306 operates to ensure thatthe current output has no negative current characteristics (i.e., all ofthe current cycles are positive). Other configurations of the bridgerectifier 306 may be utilized in accordance with the principles of thepresent invention.

A capacitor 308 may be connected to output terminals 309 a and 309 b ofthe bridge rectifier 306 for minimizing imperfections in the currentsignal from the bridge rectifier 306. In one embodiment, the capacitor308 is an electrolytic capacitor having low impedance.

The switch timing and control circuit 204 includes a switch controlelement 310 electrically coupled to the output terminal 309 b of thebridge rectifier 306. The switch control element 310 is shown as a chip.Other forms of a switching element may be utilized, includingconventional analog and/or digital circuitry. Timing circuitry 312 iscoupled to the switch control element 310 for providing switch timingand control for the switch control element 310. The values of the timingcircuitry are selected in accordance with the specification of theswitch control element 310 to provide for rapid switching of power toelectronic light generating elements. In one embodiment, the timingcircuitry 312 is selected and/or configured to enable the switch controlelement 310 to produce a switching signal (not shown) formed of asubstantially periodic pulse train signal that switches at a rate ofapproximately one thousand times per second (i.e., 1 KHz). Otherconfigurations of the timing circuitry 312 may be selected to cause theswitch control element 310 to have switching rates, either faster orslower, but that produce pulses of light output that are at a rategreater than that observable by the human eye. For example, theswitching circuitry 312 may cause the switching to occur at 500 Hz. Ingeneral, the switching rate should be greater than 100 Hz in accordancewith the principles of the present invention.

The timing circuitry 312 sets the timing periods, amplitude, and voltagelevels for the switch control element 310. The switching circuitry 312responds to the switching signal and operates to drive, in part, aswitching element 314. The switching element 314 may be a field effecttransistor (FET). In one embodiment, the FET transistor is a MOSFET asunderstood in the art. The switching element 314 responds to thesubstantially periodic pulse train signal output by the switch controlelement 310 and operates to turn current flow on and off to electroniclight generating elements, such as LEDs.

The output circuit and ripple correction circuit 208 includes acapacitor 316 and an inductor 318 that are utilized to balance thecircuit 300 a and provide inductive balance to a reactive load, such asan electronic light generating element. The capacitor 316 is optionalaccordance with the principles of the present invention because it isutilized to reduce the level of ripple current. As ripple does notadversely affect the electronic light generating elements, the use ofthe capacitor 316 is optional. However, if devices other than LEDs areutilized, ripple is compensated for by the capacitor 316. The inductorvalue may remain the same as it impacts circuit power factor, which issubstantially independent of the load.

FIG. 3B is a schematic of a circuit 300 b performing the functions ofthe modules 200 of FIG. 2 that further includes interacting with adimmer as understood in the art for increasing and decreasing the lightoutput (luminance) of the electronic light generating elements of theelectronic light bulb. A comparator 320 is coupled between the inputterminals 302 to sense a change in voltage applied by an AC dimmer 322,which also may be connected between the input terminals 302. The use ofan AC dimmer is atypical for use with a circuit for driving electroniclight generating elements that are typically controlled by a DC signal.Another fuse 324 may be included on one or both of the input terminals302.

In one embodiment, the comparator 320 operates to adjust the amplitudeof the switching element 314. To adjust the amplitude of the switchingelement 314, a comparator or feedback line may provide for adjusting theamplitude of the pulses produced by the switch control element 310. Inone embodiment, a switching pattern (e.g., pulse train) may bepreprogrammed into an application specific integrated circuit (ASIC)that incorporates components and/or functionality of the modules 200 andthe average amplitude is adjusted by altering the amplitude of theamplitude of the pulses while the frequency of the pulses is maintainedat a substantially constant rate. However, by altering the amplitude ofthe pulses driving the electronic light generating elements, it isdifficult to maintain the linearity of the dimming because of thenon-linearity of electronic light generating elements, especially ifmultiple colors of electronic light generating elements are utilized.For example, in the case of using LEDs for generating light, it isdifficult to account for the non-linearity of the diode curves of themultiple colors.

FIG. 4A illustrates an exemplary pulse train 400 for driving and dimmingelectronic light generating elements by altering the amplitude of thepulses. The pulse train 400 provides for current pulses 402 a, 402 b,402 c, 402 d, 402 e (collectively 402), etc. that are output from theswitch control element 310 (FIG. 3) and input signals to the switchingelement 314 (FIG. 3). As shown, the current pulses 402 a–402 c havemagnitudes of 100 mA and current pulses 402 d–402 e have magnitudes of80 mA, each of which have a pulse width of Δ ms. In one embodiment, thepulse width is less than or equal to 0.1 ms. Pulse frequency may be setbased on three factors, (i) output desired, (ii) size of the switchingelement selected, and (iii) electrical properties of the switchingelement selected, including switching speed. However, based onprice/performance analysis, pulse frequency may be selected between 800and 2.5 KHz. The pulses 402 may be operating at a frequency, where theperiod (P) between the pulses is 1/freq. For example, if the frequencyis 1 KHz, the period between the pulses is 0.001 seconds. However, ingeneral, the pulses 402 may be operating at a frequency at or above 100Hz to avoid flicker.

FIG. 4B illustrates exemplary output signals 404 a–404 e produced by theswitching element 314 (see FIGS. 3 and output signal 220 of FIG. 2) thatcorrespond to the pulses 402 a–402 e, respectively. As shown, the outputsignals 404 a–404 c have a peak current of 100 mA and rapidly drop off.It should be understood that the output signals shown in FIG. 4B areideal signals and that actual output signals may include delay, ripplecurrent, and noise.

Electronic light generating elements are not damaged by heating the PNjunction if the peak of the output signals exceeds the absolute maximumrated forward current (e.g., 50 mA) for a time that is generally tenpercent or less of the period P (i.e., duty cycle of ten percent orlower). However, this time range can vary depending on the parameters ofthe electronic light generating elements selected. As shown betweenoutput signals 404 c and 404 d, the magnitude of the current driving theelectronic light generating elements is lowered from 100 mA to 80 mA,which correspondingly means that the duty cycle is reduced because thepulse above the absolute maximum rated forward current is reduced. Thereduction of the duty cycle causes the luminance of the electronic lightgenerating elements to be reduced in accordance with a forward currentversus relative luminosity curve as specified by a manufacturer of theelectronic light generating elements (e.g., from 3.5 to 3.0 a.u.).

Continuing with FIG. 3B, in another embodiment, the comparator 320operates to adjust the timing of the pulses that the timing circuitproduces to drive the light generating elements. To adjust the timing ofthe pulses, an output signal (not shown) from the comparator 320 to aninput or other component that electrically communicates with the switchcontrol element 310 to adjust the rate of the pulses based on theamplitude of the input signal. For example, rather than using 1000pulses per second, the number of pulses may be reduced to 500 pulses persecond. While the pulse frequency is reduced, the pulse width andmagnitude of the pulses remains the same. This type of adjustment is notpulse width modulation as understood in the art. By reducing the numberof pulses per second, the amount of current being applied to theelectronic light generating elements remains the same from a givenpulse, but the number of pulses per second is reduced linearly. Bylinearly adjusting the number of pulses, the overall brightness of theelectronic light generating elements is linearly adjusted becauseadjusting the pulse frequency does not operate on the forward current toluminance output curve. Also, because the electronic light bulbaccording to the principles of the present invention may include threeor more colors of LEDs, adjusting the timing of the pulses maintains thesame color balance between each of the different colors because thepulse width and magnitude remains the same, but not applied current orexcited as often. In other words, because the electronic lightgenerating elements are not excited as often, the average light outputis reduced linearly, but the maximum intensity produced as a result ofeach pulse remains the same.

FIG. 5A illustrates an exemplary pulse train 500 for driving and dimmingelectronic light generating elements by decreasing the frequency of thepulse train. As shown, the pulse train includes for pulses 502 a–502 d,where pulses 502 a–502 c are spaced at a period (P) and pulses 502 c and502 d are spaced at a period (2P). In one embodiment, the period P is 1ms (i.e., frequency is 1 KHz). In accordance with the principles of thepresent invention, the pulse 502 a has a width of less than or equal to0.1 ms, which causes output signal 504 a to have a peak of 100 mA and aduty cycle above the absolute maximum forward current of 50 mA, forexample, of at most ten percent (10%) as shown in FIG. 5B. To reduce thelight output, the frequency between pulses 502 c and 502 d is reduced inhalf and the period is doubled (i.e., 2P). By increasing the periodbetween pulses, the duty cycle of the current peak above the absolutemaximum forward current of 50 mA of at most five percent (5%). Bydecreasing the frequency between pulses and maintaining the pulse widthand magnitude of the pulses, the luminance is decreased substantiallylinearly and the different colors (e.g., red, green, and blue) remainbalanced. It should be understood that the specific values above areexemplary and that different electronic light generating elements mayhave different specifications and values.

In yet another embodiment for dimming the electronic light generatingelements, a feedback circuit may be included to provide a feedbacksignal for feeding back the amount of current being applied to theelectronic light generating elements from the switching element 314. Infeeding back the information to indicate the amount of current drivingthe electronic light generating elements, a simple current feedback loopmay be utilized as understood in the art. By feeding back the current,accurate control of the amount of current being applied to theelectronic light generating elements is maintained so that linear lightdimming control may be maintained even given the non-linearity of lightoutput in response to forward current applied to the electronic lightgenerating elements.

FIG. 6 illustrates a CIE chromaticity diagram 600 as understood in theart. LEDs and other electronic light generating elements are typicallyspecified in terms of CIE chromaticity wavelengths. By combiningmultiple electronic light generating elements, specific shades of whiteor other colors of light maybe produced by an electronic light bulbcontaining the multiple electronic light generating elements. Electroniclight bulbs may be populated with specific color electronic lightgenerating elements for specific purposes. For example, a light that isinvisible for bugs may use electronic light generating elements havingwavelengths above 490 nanometers. By selecting and using electroniclight generating elements in the electronic light bulb, the need to usean optical filter is eliminated. It should be understood that otherspecific purpose electronic light bulbs may be produced. For example,electronic light bulbs that produce UV light, at least in part, may beproduced by selecting and populating the electronic light bulb with theproper electronic light generating elements.

The innovative concepts described in the present application can bemodified and varied over a wide rage of applications. Accordingly, thescope of patented subject matter should not be limited to any of thespecific exemplary teachings discussed, but is instead defined by thefollowing claims.

1. An apparatus comprising: an electronic light generator having amaximum current rating; and a circuit producing an electric signal thatdrives said electronic light generator, said electric signal including apulse train that has a plurality of first pulses and a plurality ofsecond pulses, the amplitudes of said second pulses being less than theamplitudes of said first pulses, and said pulse train being configuredas successive groups of pulses that each start with one of said firstpulses and that each include at least one of said second pulses, atleast some of said pulses of said pulse train having a peak currentvalue above said maximum current rating, said output signal being inexcess of said maximum current rating less than ten percent of the time.2. The apparatus according to claim 1, wherein said pulses each have arise time to a peak value, and have a fall time from the peak value thatis longer than the rise time.
 3. The apparatus according to claim 1,wherein said groups have respective time durations that areapproximately equal.
 4. The apparatus according to claim 1, wherein saidcircuit selectively varies a frequency of said pulse train.
 5. Theapparatus according to claim 1, wherein each said group includes atleast two of said second pulses.
 6. The apparatus according to claim 1,wherein said electronic light generator is a light emitting diode.
 7. Amethod comprising generating a electric signal for driving an electroniclight generator having a maximum current rating, said electric signalincluding a pulse train that has a plurality of first pulses and aplurality of second pulses, the amplitudes of said second pulses beingless than the amplitudes of said first pulses, and said pulse trainbeing configured as successive groups of pulses that each start with oneof said first pulses and that each include at least one of said secondpulses, at least some of said pulses of said pulse train having a peakcurrent value above said maximum current rating, said output signalbeing in excess of said maximum current rating less than ten percent ofthe time.
 8. The apparatus according to claim 7, wherein said generatingincludes causing said pulses to each have a rise time to a peak value,and to have a fall time from the peak value that is longer than the risetime.
 9. The apparatus according to claim 7, wherein said generatingincludes configuring said groups to have respective time durations thatare approximately equal.
 10. The apparatus according to claim 7, whereinsaid generating includes selectively varying a frequency of said pulsetrain.
 11. The apparatus according to claim 7, wherein said generatingincludes configuring each said group to have at least two of said secondpulses.
 12. The apparatus according to claim 7, including selecting alight emitting diode to serve as said electronic light generator.